1. Technical Field
The present invention generally relates to alkylation. More particularly, the present invention relates to a high shear system and process for accelerating alkylation of a feedstock comprising isoparaffins and olefins thereby increasing the octane number of the feedstock.
2. Background of the Invention
It is well known in the petroleum refining arts to catalytically crack heavy petroleum fractions, such as vacuum gas oil, or even in some cases atmospheric resid, in order to convert a substantial proportion thereof to a wide range of petroleum fractions. The light products from hydrocracking are rich in isobutane. Isobutane is a primary feedstock for motor fuel alkylation processes, which produces an excellent and environmentally superior gasoline-blending component.
Early alkylation units were built in conjunction with fluid catalytic cracking units to take advantage of the light end by-products of the cracking units: isoparaffins and olefins. Where the petroleum fraction being catalytically cracked contains sulfur, the products of catalytic cracking will also likely contain sulfur impurities. Hydrotreating is used for removal of undesirable components, including sulfur and nitrogen.
In general, hydrofinishing of FCC gasoline lowers the octane number thereof. Smaller molecules such as isobutane and propylene or butylenes can be recombined to meet specific octane requirements of fuels by processes such as alkylation or less commonly, dimerization. Octane grade of gasoline can also be improved by catalytic reforming, which strips hydrogen out of hydrocarbons to produce aromatics, which have much higher octane ratings.
Alkylation is the process of reacting light olefins with iso-butane to produce an alkylate product high in iso-octane. In alkylation, an alkyl group is added to an organic molecule (typically an aromatic or olefin). Thus an isoparaffin can be reacted with an olefin to provide an isoparaffin of higher molecular weight. Industrially, the concept depends on the reaction of a C2 to C5 olefin with isobutane in the presence of an acidic catalyst to produce an alkylate. This alkylate is a valuable blending component in the manufacture of gasolines due to its high octane rating and sensitivity to octane-enhancing additives. This motor fuel alkylate, which is ideal for producing reformulated gasoline, is suitable for gasoline blending because of its high octane and low vapor pressure.
Alkylate gasolines, such as those produced by the processes discussed above, are rich in isoparaffins and contain essentially no sulfur and aromatics. Generally exhibiting strong sensitivity to octane-enhancing additives, alkylate gasolines are prime candidates for blending into motor gasolines to meet increasingly stringent environmental regulations restricting gasoline vapor pressure and aromatics content. However, these alkylate gasolines are not suitable for use as blending stocks until they are free from the acid components of the alkylation catalyst. Specifically, the Lewis acid component of the alkylation catalyst complexes employed in common processes must be removed before the alkylate product can be blended into gasoline.
Standard alkylation processes have a continuous acid phase. However, U.S. Pat. No. 5,345,027 describes an alkylation process comprising a viscous acid catalyst dispersed in a continuous hydrocarbon phase.
Accordingly, there is a need in the industry for improved processes and systems for the commercially important alkylation of isoparaffins.